1. Field of the Invention
This invention concerns a method of treating radioactive wastes mainly composed of various combustible and/or poorly combustible organic materials, or mixtures thereof with inorganic materials.
2. Description of the Prior Art
Various kinds of radioactive organic waste are generated in nuclear power plants and facilities handling radioactive substances. At present, some of these wastes are partially treated, but most are left untreated. That is, the waste is charged and stored in an untreated state in drums or other containers. Filtration aids, spent ion exchange resins and the like, are stored, as they are, along with liquid waste in storage tanks.
The amount of radioactive wastes generated will increase over time, and the places or facilities for storing accumulated radioactive wastes will inevitably be filled up. Furthermore, when solid radioactive wastes are stored, as they are, mixed with liquid waste in storage tanks, safety problems may arise. Accordingly, there is an urgent demand for developing end establishing a practical treating method for solving these problems.
Various methods of treating radioactive wastes, such as, compaction, incineration and acid digestion, are now under development or have been put to practical use. However, these waste treatment methods have serious drawbacks which limit their utility. The compaction method does not exhibit an effective volume-reduction ratio of the treated radioactive wastes, and therefore does not satisfactorily minimize the required waste storage space. Furthermore, the substances which can be processed by the compaction method are limited. Referring to the incineration method, there is an additional requirement for facilities to seperate and remove sulfur oxides, nitrogen oxides, chlorine, hydrogen chloride and fine ash that are contained in a large volume in the gaseous wastes generated during incineration. Also, secondary radioactive wastes are generated from the treatment or the geseous wastes. Therefore, in the incineration method, the volume-reduction effect of the treatment is offset by the above named problems and another problem is caused by corrosion or the incineration facilities.
There has been well known a wet oxidation process which is employed in the treatment of liquid wastes containing ordinary organic substances, in which the liquid wastes are continuously introduced into an oxidizing reactor at a high temperature end high pressure end are subjected to air oxidation. However, the oxidizing reaction tends to be terminated at the formation of organic acids in this method. As a means for avoiding this defect and improving the degree of oxidation, it has also been known that the addition of a catalyst, such as copper ions, is effective for oxidizing the organic substances more completely. It may be possible to apply such a conventional continuous wet oxidizing process to radioactive organic wastes. However, there have been various drawbacks such as (1) the degree or oxidation or the organic meterials is low, (2) a great amount of waste water containing radioactive substances end heavy metals used as the catalyst are discharged thereby creating various problems in the treatment or the discharged waste water and (3) if thermoplastic high molecular polymeric substances are contained in the radioactive wastes, they will be melted in the reactor and fused together (hereinefter referred to as fusion) with other organic wastes, thereby forming large lumps which hinder the progress of the oxidizing treatment. Because of these drawbacks, application of the wet oxidizing process to treat radioactive wastes has not yet been put to practical use.
It is usually difficult to treat a waste mixture, at the location at which it is generated, to separate it into its respective kinds of components and discharge them separately. Similarly, it is more difficult, if not impossible, to subsequently treat a waste mixture to separate those different kinds or components. If the wastes contain naturally radioactive substances, this difficulty is increased more remerkably.